Block signaling system for railways and the like



1.. H. PETER EI'AL 2,320,793 I BLOCK SIGNALING SYSTEM FOR RAILWAYS AND THE LIKE Filed March 17; 1942 4 Sheets-Sheet 2 M. %w\\ H N WSMQ AMER E QMQQ QSQN ik wk wwm m +L ikmm w June 1, 1943.

, swmxwv 88% QERQ wmw Patented June 1, 1943 BLOCK SIGNALING SYSTEM FOR RAILWAYS AND THE LIKE Leslie Hurst Peter and James Perrin Coley, Kings Cross, London, England, assignors, by mesne assignments. to The Union Switch & Signal Company, Pennsylvania Swissvale, Pa.,

a corporation of Application March 17, 1942, Serial No; 435,084 In Great Britain May 20, 1940 9 Claims. 1 (01. 246-26) the entrance of the train into the section together with automatic indications of the subsequent progress of the train are effected by coded current impulses, the improved system ensuring a high degree of safety in operation and requiring only a single line circuit connecting the two "signaling instruments.

According to the principal feature of the invention the transmission of each current impulse" constituting a code element, except the first element of a code signal, is arranged to be dependent upon and effected by the proper transmission of the preceding code element, the indication corresponding to the code signal being only efiected when the code signal has been fully completed.

The invention is illustrated by way of example in the accompanying drawings of which Figure 1 is a diagrammatic view of a section of railway track between points A and B at which apparatus arranged in accordance with one form of the invention is provided. Figure 2 is a view of the line circuit between the points A and B and its associated apparatus. Figure 3 illustrates portions of the apparatus and circuit connections at the point A of the system, the similar portions of the apparatus at point B being omitted for the sake of simplicity. Figure 4 is a view in front elevation of the signalling instrument provided at each of the points A and B, Figure 5 illustrating diagrammatically the construction and circuit connections of the signaling instrument at the point A. Figures 6, '7, 8, 9, 10, ll, 12, 13 and 14 illustrate the circuit connections of portions of the apparatus at the point A of the system. Figures lla and 12a show release lever K and signal lever SB, respectively, together with their locking segments, the lock magnets and circuits for which are shown in Figures 11 and 12. The

arrangement of signal lever S5 and its locking segment, the lock magnet and circuit for which are also shown in Fig. 12. is the same as shown in Fig. 12a for lever Si), and is therefore omitted from the drawings.

Referring now to the drawings the system illustrated is adapted for the transmission between points A and B at the ends of a section of track "as shown in Figure '1 of the signals is line clear received, line clear, line closed, and train on line coming. These signals when received are exhibited on a signaling instrument (illustrated in Figures 4 and 5) at each end of the section, these instruments being also adapted to exhibit the signals line clear sent and train on line going. Each instrument also comprises a press button I for transmitting the signal is line clear, a small signal lamp 2 for indicating the reception of this signal together with a cancel press button 3 for transmitting a request to cancel a previous signal and an indication. lamp 4 for notifying that a cancellation operation is required. Adjacent to each of the points A and B in the section of track a short insulated section of the track AXT, BXTis provided to which current is supplied, each of these track'sections being provided with a track relay XTR and YTR, respectively, which is utilised to efiect the autoy matic transmission of a signal as will be described later.

The section of track is also provided adjacent to each of the points A and B with starter signals 5, 6, I, 8, a release lever K provided with electric locks KK and contacts KA, KEl (see Figures 11 and 11a) closed in certain positions of the release lever.

The signaling instruments at A and B are electrically connected by means of a line circuit comprising two conductors 9, B0 (or a conductor and earth return), a battery ALB and IBLB respectively being provided at the two ends of the line circuit from which current'is derived to produce code impulses or elements. i

The apparatus at each of the points A and 13 also comprises a slow release master relay M, a normally de-energised relay R, a slow release relay SR for the instrument at A and a similar relay QR (not shown) at B, the release time of the relay SR being however'considerably greate than the release time of the relay QR.

. Connected in the line circuit at each end of the section are positive and negativeline relays BL and 'NL, the former of which is responsive only to current of positive polarity or direction, the relay NL being similarly responsive only to current of negative polarity or direction.

The apparatus at each' of the points A and B also comprises aslow acting line closed relay LC and a slow acting line open relay LO togetherfwith a chain of counting relays 2A,-'2 B, 3A, 313, 4A, 13, a set of register relays ZBS, SBS

and ABS for positive impulses and a similar set of register relays ZNS, 3NS and 4NS for negative impulses.

Each of the signaling instruments is also provided with a set of receiving relays ARLC, ARTOLC, ALRB, ARCR, ARLBK, ARC and ARILC of which relays ARTOLC and ARILC are of the latch type adapted to operate to their energised positions by current supplied to the upper coils of the relays and mechanically latched in these positions until released by current supplied to their lower coils.

The system also comprises at each of the points A and B a set of transmitting relays ATC, ATCR, ATLB, ATLBK, ATTOLG, ATILC, and ATLC together with certain other relays which will be referred to in describing the operation of the system. It will be understood that these relays are only shown for the point A of the system and that the corresponding relays for the other point B hereinafter referred to bear the prefix B instead of the prefix A. Thus for example the relay ATO at A corresponds to a similar relay BTC at B.

Each of the codes employed consists of four code elements of which the first is invariably a positive element, the remaining elements being positive or negative so that eight codes in all can be transmitted.

The various impulse combination as regards the 2nd, 3rd and 4th impulses are allotted to the difierent signaling indications to be transmitted as follows:

, Code elements Signal transmitted 2nd 3rd 4n;

' Is line clear from A to B and B to A.

+ Train on line coming" from B to A and line clear from A to B. Line closed indication from B to A and train on line coming from A to B. Line clear" from B to A and line closed" from A to B. Line closed from B to A and line closed indication from A to B. Line clear received."

The indicator portion of each of the signaling instruments at A and B is of the moving coil armature type comprising (as shown in Figure 5) an armature ll surrounded by an energising coil l2 and rotatably mounted in a magnetic field produced between the pole pieces of a permanent magnet IS. The armature is normally retained, by means of suitable springs M, in a central position in which a pointer l5 secured thereto .4) the pointer l5 indicates line clear sent while when this current is of considerably higher strength the armature H is moved to a further position in which the pointer I5 indicates train on line coming. Fora negative current of predetermined strength traversing the armature coil ii the armature H is correspondingly moved in the opposite direction to a position in which the pointer I5 indicates line clear received or if the current is ofa higher strength to a position in which the pointer I5 indicates train on line going. The polarity and magnitude of the current transmitted to the energising coil [2 on the armature of each instrument are dependent upon the energisation of certain relays which as regards the indication line clear sent from the points B or A are energised by the action of the Signalman. In the case of the indication line clear received, on the other hand, the relay controlling the supply of current to the energising coil I?! of the instrument is energised only at the conclusion of the corresponding code. The current thus supplied in both cases to the energising coil E2 of the instrument is of a predetermined lower value the circuit of the coil including under these conditions suitable resistances RI and R2.

As regards the energising coil of the instrument giving the indication train on line going the indication is efiected by the train itself entering the short insulated track section AXT or BXT, the indication train on line coming at the other point being effected by the action of the relay ARTOLC which is energised only on the completion of the corresponding code, the circuit of the energising coil ll of the instrument under these conditions not including the resistance RI or R2 so that the current is of a corresponding higher value. As regards the indication line closed in which the energising coil [2 of the instrument is not traversed by current, this is eiiected either under normal or in-operative conditions of the system or by the train leaving the short insulated section AXT or BXT adjacent to the points A or B.

Under normal conditions, that is to say, when the section of track is closed or blocked for traffic, the line circuit and the various relays at both ends of the section are de-energised, circuit proving relays ANPR. and BNPR being latched up. The pointer I5 of each signaling instrument occupies its normal position (as shown in Figure 4) So as to give the indication line closed. The release lever K at each end of the section is locked in its normal position.

In general the operation of the system is as follows:

The signalman at the point A or B Wishing to despatch a train from this point to the other point, transmits through a relay ATILC or BTILC a code signal which when properly received effects through the energisation of a relay ARILC or BRILC the illumination of the signal lamp 2 indicating is line clear. The Signalman at the other point upon receiving this signal and if prepared to receive the train then, by-operating the release lever K, transmits through a relay ATLC or BTLC a code to the other point, this code when properly received effects the energisation of a relay ALCS or BLCS causing a corresponding indication line clear sent to be given at his signal instrument and of a relay ARLC or BRLC causing the indication line clear received? at the other instrument and permitting the starting signal to be operated.

The starting signal having been cleared the train then proceeds from the point A or B towards the other point and upon entering the short track section AXT or BXT effects automaticall through the relay ATTOLG or BTTOLG the transmission of a code signal to the other point by causing the signal instrument there to indicate through a relay ARTOLC or BRTOLC train on line coming the indication train on line going being caused to be given at the point from which the train is leaving by the action of a relay A'IOLG or BTOLG controlled by the entrance of a train into the insulated track section AXT or BXT.

Assuming for example that it is desired to despatch the train from A to B, the signalman atA will accordingly transmit the signal is line contacts of a code cutout push button IE to negative.

Relay A'I'ILC being thus energised completes its own stick circuit from positive, relay back contact 434, through wire I! and front contact ATILC2.

Relay SR is now energised (see Figure 14) from positive through relay back contacts BLP4,

NLPI and relay front contacts ANPRA and ATILCI and coil of relay SR to negative.

It will be seen from Figure 14 that relay SR is similarly energised when any other of the relays ATLB, ATTOLG, etc., is energised during a code transmission.

Relay BT at the point A is now energised from positive through front contact SR2 and coil of rel'ay BT to negative and the line circuit 9, I

is thus positively energised from battery ALB through relay front contacts BTI, and BT2 (see Figure 2). During the operations at A above described the relays at B remain deenergised, the proving relay BNPR (like its corresponding relay ANPR) being however latched up in its energised position.

The first positive step of the code is now transmitted to the point B in the following manner.

Relay BL at point A is energised by line current and energises repeaterrelay BLP through an obvious circuit. I

. Relay M at A (see Figure 13) is energised from positive through relay front contacts BT6 and BLP5, coil of relay M and back contact R4 to neg- :ative. At the same time; relay LC (Figure 2) is energised from positive through front contact BLP6, back contacts NLP4 and MP1, front contact ANPRI and. coil of relay LC to negative. Two stick circuits are provided for relay, LC, via, one through front contacts ANPR5 and LCI3 and the other through front contact BLP6, back contact NLP4 and front contact LC9.

Relay LC being energised, a stick circuit for relay M is completed (Figure 13) from positive through front contacts LClll, BT3, BLZ and M2.

At the point B the operation above described will have caused the relay BL to be energised which in turn energises its repeater relay (not shown' but corresponding to relay BLP at A);

.The relay M at B will remain de-energised but relay LC at B will be energised and its second stick circuit through front contact BLP closed as above described for relay LC at A.

A circuit is now completed for relay R at B (see lower part of Figure 13) from positive, front contact L04, back contact M4, front contact BLPZ, back contact BT5 and coil of relay R to negative. A stick circuit for relay R is then completed through front contact R5.-

The energisation of relay BLP at A'will open the circuit of relay-SR at back contact BLP4 and circuit completed in a similar manner.

'relay SR will accordingly release at the end of its slow releaseperiod and will open the circuit of relay ZBT at contact SR2 (Figure 2). The release period of relay SR thus determines the duration of the first code impulse.

The deenergization of relay BT at A opens the line circuit at contacts BTI and BTZ so that the relay BL will release and release relay BLP.

At the point B relays BL and BLP will similarly release.

At the point A the release of relay BLP will complete a circuit for relay L0 from positive through back contacts BLP6 and NLP5, front contacts LCI and ANPR2, coil of relay L0 to negative. Relay LO being thus energized another circuit for this relay coil is completed through contact LOI shunting contact ANPR2 while a circuit for the release or lower coil of relay ANPR is completed through front contact L05. Relay ANPR is thus unlatched and releases completing a circuit for relay LOP from positive, front contact L03, back contact ANPR3 and coil of relay LOP to negative. It will be noted that for the energization of relays SR, LC and LO the proving relay ANPR must be latched in its energized position to which it will have been set as will be described later.

At the point B, relay L0 is energized, relay BNPR released and relay LOP energised in the same manner as that above described for the corresponding relay at point A.

At the point A a circuit is completed for energising relay 2A from positive through relay front contacts LCZ, LOPZ and L04, the continuity contacts of relays 43, 4A, 3B, 3A and 2B, coil of relay 2A to negative.

At the point B the corresponding relay 2A is energised in a similar manner and the first code step is completed.

At the point A, the second code step begins by the completion of a circuit for energising relay BT from positive through front contacts M5 and 2A3, back contact 2B3, wire I 9, front contact ATILC3 and coil of relay BT to negative. Relay BT being thus energised, relays BL and BLP at points A and B are energised as described for the first code step.

It should be noted that slow release relay LC although de-energized by the previous release of relay BLP has not released until relay BLP is again energised. In the event however of the line circuit remaining open for longer than the release period of relay LC, the release of relay LC will prevent further code transmission until relay ANPR is reset by a negative current impulse.

Similarly, slow release relay LO will notrelease until its release period has expired after which relay LO will release and will release relay LOP. The slow release feature of relay M will prevent its release during the interval between relays BT and BLP being de-energised and re-energised.

At point A, a circuit will now be completed for relay ZBS from positive through front contacts LOP4, L05, LCB and BLP 3, back contact NLP3,

- "front contact 2A5 and coil of relay 2B8 to negative, a stick circuit for this relay being completed from positive throughffront contacts LCB, L0! and ZBSI.

At point B relay ZBS is energised and its stick At point A the energisation of relay ZBS completes a circuit for relay 23 from positive through front contacts LCS, L01, ZBSZ, 2A! and coil'of relay 2B tonegative; The energisation of relay -2B opens the circuit for relay 2A at. continuity contact 2B! and completes a stick circuit for relay 2B through the circuit for relay 2A.,

The energisation of relay 2B and the release of relay 2A de-energises wire l9 so that relay ET is de-energised and releases relays BL and BLP.

At the point B relays BL and BLP are similarly released and the second. code step is completed.

The third code step now begins by a circuit eing completed for relay 3A at the point A from positive through back contacts BLP 8 and NLP 8, front contacts LCI I and L02, back contacts B'I' l, N'I4 and 2A2, front contact 2B2 and coil of relay 3A to negative. The circuit of relay 2B is broken atcontinuity contact 3A] and relay 3A is maintained energised through a stick circuit previously maintaining relay 2B.

At the point B relay 3A is energised and its stick circuit completed in a similar manner relay 2B being de-energised. At the point A, a circuit is-cornpleted from positive-through front contacts M and 3A4, back contact 334, wire 29, front contact ATILC4 and coil of relay BT to negative.

The energisation of relay BT causes the energisation of relays BL and BLP at both the points A and B.

Relays BLP being energised at points A and B, the relays SBS at these points are then energised and their stick circuits completed in a similar manner to that above described With reference to relays ZBS, and energising and stick circuits are completed for relays 33 at both points A and B the circuits of relays 3A being broken at continuity contact 3Bl.

The consequent release of relays 3A effects the release of relay BT at point A which causes the release of relays BL and BL? at both points, thus completing the third code step.

The fourth code step now begins by the energisation of a circuit for relay 4A from positive through back contacts BLPB and NLP8, front contacts LCI l and L02, back contacts BT 3, NT4, 2A2, 2B2, 3A2 and front contact 3B2 and coil of relay 4A to negative.

Relay A being energised breaks at its con tinuity contact 4A[ the circuit for relay 3B and a stick circuit for relay 4A is completed in the manner already described.

At the point B, relay 1A is energised and its stick circuit completed and relay 3B released in the same way.

At the point A a circuit is completed from positive through front contacts M5 and 4A4, back contact 4B5, wire 2i, front contact ATILC5 and relay BT to negative.

. Relays BL and BLP at points A and B are thus energised as before completing energising and stick circuits for relays ABS at both points.

' A circuit is now completed at point A for relay 4B from positive through front contacts L06, L01 and lBSZ, back contact R8, front contacts ATILCS,. GBSQ, SBST, EBSE wires 22 and 23, front contact 4A2 and coil of relay GB to negative.

The corresponding circuit for relay 4B at point 'B is completed from positive through front contacts L05, L01, 4BS2, R3, wires 24 and 23, front cont-act lA2 and coil of relay 4B to negative.

the relays BL and BLP at both points A and Bare thus'released completing the fourth and last code step.

, At the point A the energisation of relay 4B breaks the stick circuit for relay ATILC at contact 434.

At the point B delivery relay D is energised from positive through back contacts BLP8 and NLP8, front contacts LCII and L02, back contacts BT4, NT4, 2A2, 2B2, 3A2, 3B2 and 4A3, front contacts 4B2 and R1 and coil of relay D to negative.

At the point A, relay LC releases after its time period breaking the circuits for relays LO, 4B and M. These relays are thus released, relay LO releasing relay LOP.

At the point B, relay LC eventually releases and relays LO andD being thus de-energised, release and release relay LQP which in turn releases relay R.

In the meantime the energisation of relay D completes a circuit for relay BRILC from positive through front contacts D3, 2BS3, wire 25, front contacts 3BS4 and 4BS6, back contact BRLBK3 normal contact KN of lever K, coil of relay BRILC, wire 26 and back contacts BTC9 and BTCR8 to negative.

Relay BRILC is thus energised and is latched up.

The release of relays D and LC at the point B breaks'the stick circuits for the code storage relays ZBS, 3BS. and 4BS which accordingly release while the release of relay LC deenergises relay 4B.

During the release period of relay R, that is, when relays LO, L0 and LOP are deenergised but relay R has not yet released, a circuit is completed from positive through front contact R3, back contacts LCI2, LOIB, LOP3 and coil of relay NT to negative.

The energisation of relay NT at point B causes the line circuit 9, N to be supplied with negative current from battery BLB through contacts NTI and NT2 and the relays NL and NLP at points A and B are thus energised.

At the point A the proving relay ANPR. is now energised from positive through back contacts M5, R2, 2386, 2NS8, 3BS8, 3NS1, 4BSIO, 4N S8, 432, D4, LOP5, L08, L01, front contact NLP9, the upper coil of relay ANPR to negative.

Relay ANPR at point A is thus energised and latched, relay BNPR at point B' being similarly operated.

At the point B when relay R eventually releases the relay NT is deenergised and relays NL and NLP at both points are then released.

All the relays are now deenergised but atpoint B relay BRILC is latched in its energised position in response to the completion of the code signal is line clear" sent front point A.

The operation of the system during the four steps of a code signal transmission having been described in detail as regards the signal is line clear resulting in the energisation of the corresponding relay BRILC at the point B, it will be understood that the transmission of the other code signals is effected by a similar series of relay operations at each step resulting finally in the energisation of a relay of the group in which the relay BRILC is included.

The complete operation of sending a train from point A to point B will now be described.

The signalman at A first actuated the press button I to effect the latching of the relay BRILC as above explained in detail. As a result the lamp 2 and a bell 21 are supplied with operating current through a circuit (see Figure 7) from positive, front contact BRILC3 and lamp 2 and bell 21 to negative.

When the signalman at B is in a position to give line clear to A, he reverses his release lever K, this being possible by the energisation of the normal lock KK over front contact BRILC l (see Figure 11), providing no other code is on the line. Reversal of this lever K energises relay BTLC, provided that the coding equipment is at rest, as indicated by back contacts of relays LC, L and BLP in the pick up circuit. The circuit may be traced (see Figure 2) from positive through back contacts L09, L08, BLP I, BTOLCH, BRTOLCZ, BTLBK3, BRLBK2 reverse contact on lever K, front contact BRILC coil of relay BTLC, back contacts 1 of relays BTC, BTCR, the code cut out button IE to negative.

A stick circuit for relay BTLC is completed through back contact 4B4 and front contact BTLC2. Energisation of relayBTLC energises latch coil of relay BRILC at front contact BTLCI, so releasing this relay, breaking the pick-up circuit of relay BTLC, and stopping the bell 2'! which has been ringing since the is line clear indication lamp 2 was illuminated.

Relay BTLC will then initiate a code transmission energising relay ARLC, providing relay BRILC has released as arranged for, by back contact BRILCI in the second step code selection circuit. It will be noted that Bs release lever K is locked in the reverse position, after the release of relay BRILC, also, on completion of the line clear code transmission, relay BLCS is energised through a circuit (see Figure including front contacts of 4B9 and BTLC9, coil of relay BLCS, back contact BTC8 to negative, and sticks up through back contact BTROLC8 and front contact BLCS2.

At the point B, energisation of relay BLCS connects positive to the instrument at front contact BLCS4, through resistance RI, coil l2 of the instrument, resistance R2, back contact LBRLCP4, and front contact BLCS3 to negative, thus moving the instrument to line clear sent.

Relay ARLC sticks up through an obvious stick circuit provided that both the starting signals are at danger as determined by contacts NB of the levers controlling these signals. Relay ARLCP (see Figure 6) now picks up, through a circuit including front contact ARLCB, and sticks up over back contact ATTOLG'I and front contact ARLCP3.

Energization of relay ARLCP connects positive to the instrument over front contact ARLCP4 resistance R2, coil l2 of the instrument, resistance RI, and over front contact ARLCP5 to negative, the instrument thus moving to line clear received.

Operation of one of the starting signals releases relay ARLC by breaking the stick circuit at the contacts NB, but picks up relay 6/5SS through a circuit including front contact ARLCPZ. An obvious stick circuit including front contact 6/5SS2 is then completed.

Nothing further occurs until the train passes the starting signal 5 or 6 and de-energises the fouling track circuit AXT. The corresponding track relay XTR releasing, picks up relay ATI'OLG, over front contact 6/5582 and back vontact X'IRl of the track relay. When relay ATTOLG picks up, relay ARLCP is released, as the stick circuit is broken at back contact 1. In addition, relay 6/5SS is released, as the return circuit is broken at front contact ARLCP2.. It will be seen that the release of relays ARLCP and 6/5SS are checked in the transmission code selection for the second impulse at back contacts ARLCPI and 6/5SS3. When this transmission is complete, relay ATOLG picks .up (see Figure 10) over front contacts relay 439 and ATTOLG9 and latches.

Referring again to Figure 5 it will be seen that relay ATOLG connects positive direct on to the instrument at front contact ATOLG3, and negative at front contact ATOLGG, thus moving the instrument to .train on line going.

The starting signals can now be replaced.

Receiving relay BRTOLC picks up and latches up in response to the transmission initiated by relay ATTOLG, and relay BRTOLC opens the stick circuit for relay BLCS (see Figure 10) at back contact BRTOLC8. In addition positive energy is applied to the instrument at B through front contact BRTOLCIll and BRTOLCS. The instrument now moves to train on line commg.

When the train clears the fouling track, the track relay picks up again, but without causing any effect except the release of relay XTPR.

The signalman at B should now clear his home signal HKB .(see Figure l), which picks 1119 relay HSS over the reverse contact HBR on the home signal lever, and which sticks up over back contact 4 of relay YTHSSP (corresponding to relay XTHSSP at point A) and front contact 4 of HSS.

When the train reaches the track section BXT the track relay releases so energising relay YTPR (corresponding to relay XTPR at A). The home signal may now be replaced at any time; there is no lock on the home signal lever.

When the train clears the track section 'BXT the track relay picks up and opens the circuit for relay YTPR. As this relay has a delayed release, a circuit is made over front'contact l of YTR, front contact 2 of relay I-ISS, front contact I of relay YTPR, coil of relay YTI-I'SSP to negative, in sufficient time for relay YTI-ISSP to pick up and stick up over back contact 3 of BTLB and front contact I of YTHSSP. Energisation of this relay breaks the stick circuit for relay HSS at back contact 4. Should the home signal be restored to normal relay BTLB now picks up over a circuit from positive, front contact 3 of relay BRTOLC, back contact 3 of relay HSS, normal contact on levers of signals HB, front contact I of relay YTHSSP, coil of relay BTLB, back contacts 1' of relay BTC and BTCR, code out out [6 to negative,,and sticks up over the relay 43 released as usual. The release of relay YTHSSP is proved in the transmission at back contact 3.

Relay ARLB will pick up in response to the transmission and stick up over back contact of ATLBKH and front contact 4 of ARLB.

A circuit is now completed from positive through back contact ALCSl, normal'contacts SGN and SEN on levers of signals 6 and 5f front contact ARLB3, coil of ATLBK, back contacts ATCI and ATCR'I, code out out button over relay back contact 4B4. This relay opens I 6 to negative, the stick circuit being as usual the circuit for relay ARLB at back contact ll, so releasing it.

A slow release feature is provided on relay ATLBK, to enable therelay to hold upfor sufficient time at the completion of the .r'ansmission, for the latch circuit for relay ATOLGto be made over front contacts 41B! and of ATLBKB (see Figure 10). The release of relay ARLB is proved in the transmission at back contact I.

Release of relay ATOLG breaks the circuit to the instrument indicator and allows it to return to the line closed position.

Relay BRLBK is now energised at Band sticks up over a KRD contact'on the release lever K. This releases the reverse lock on the release lever (see Figures 11 and 11a), allowing this to be restored so de-energising relay BRLBK. Also, when relay BRLBK is energised, it completes the circuit for the latch coil of relay BRTOLC at front contact BRLBK4, so deenergising relay BRTOLC and returning the instrument to normal or line closed.

The prevention of opposing moves at the points A and B is effected as follows:

The release lever K must be in its normal position to pick up relay A'IILC in order to initiate a code for is line clear, but it is also required in the reverse position in order to send the line clear code, and a glance at the circuits will show that it cannot be returned to its normal position until relay ARLBK picks up to make its front contact 8, in -order that the reverse lock KK on the release lever K may be energised to permit the lever to be returned to normal,

We now have the condition that lever K has been reversed in order to send line clear to B and that it cannot be returned to normal (a necessary condition for the sending of is line clear) until relay ARLBK is energised. It will also be appreciated that B cannot send line clea to A until he receives is line clear from A; since the circuit for relay BTLC at B is broken at a front contact of BRILC.

Now relay ARBLK picks up only in response to a code sent from B to prove that line closed has been received from Aand, as line closed is sent from A to B when the train has cleared the section, it follows that, once A has operated his release lever to send line clear to B, he cannot return it to normal,and therefore cannot send is line clear to B, until the train has passed right through thesection. It 'is therefore ensured that line clear cannot be given for opposing moves 7 As regards following moves the prevention of these is effected-as follows:

When A receives line clear from B, relay ARLC picks up and sticks up over NB contacts on the two starting signal levers S5 and S6. When an attempt is made to operate the lever to clear say signal 6, the lever can be moved to its (B) position where it is held by the lever lock KS5 (see Figures 12 and 12a). There is now a circuit over front contact ARLCA to energise the lever lock, and the lever can be operated. Once it is taken past the (B) position, relay ARLC releases. Relay ARLC can now be picked up only on the receipt of another line clear code from B, so that, once the signal lever is replaced, it

cannot again be pulled until permission is received from B.

In the event of the is line clear button I at points A and B being operated so nearly at the same time that thetrans'mitter relays BT at each point pick up simultaneously, the system is so arranged that under these conditions the code from point A-takes precedence.

When the BT relays pick up simultaneously at thepoints A and B, thetwo batteries ALB and BLB are connected inseris arfd'the twoBL *relays pick up on double current. But relay QR at B releases some time before relay SR at A 'due to their diifere'nce in slow release, hence when QR releases it opens the circuit for BT at B, but BT releasing only cuts out battery BLB, so that the BL relays are maintained energised over the front contact of BT at A receiving energy from battery ALB.

Thus at point B, front contacts 3 and '6 or relay BT are open, while front contact '2 of relay BL remains closed; hence the circuit for rela'y M is open and this relay releases at B and relay R picks up.

At point A however, both relays BT and BL remain energised until slow release relay SR releases, so that relay M remains energised.

It will be understood that the invention is not limited to the particular system above described and illustrated by way of example which may be varied and amplified in many respects without exceeding the scope of the invention.

Having now described our invention, what we claim as new and desire to secure by Letters Patent is:

1. In a signal control system for a stretch of single railway track in which signals are located at opposite ends of the stretch for governing traffic movements over the stretch, the combination comprising, manual control apparatus located adjacent each of the opposite ends of said stretch each includin'g a inanu'ally controllable contact device freely operable at any time and a second manually controllable contact device having a normal 'an'd'a reverse position and said second contact device having a normal lock for looking said second contact device in 'the'normal position if'said nor'm'al lock is 'deen'e'r'gize'd, a pair of control conductors extending between the opposite ends of said stretch, 'means controlled by operation of one of said first contact devices if the adjacent second contact device is in its normal position for transmitting a code over said conductors 'to the apparatus at the opposite end of said stretch'for efiecting an indication is line clear at said opposite end of the stretch and for energizing the 'lock for the second contact device at'said'oppositeend of the'stretch, means controlled bythe second contact device at said 0pposite end of the stretch if then operated to its reverse position for transmitting a codeover said conductors to the first 'end of the stretch for effecting a line clear indication at the first end of said stretch, and means for clearing a signal at the first end of said stretch if the line clear indication "has-been received.

'2. In a signal control system for a stretch of railway'trackin which signals are located at opposite ends of the stretch for governing traffic movements over the stretch, the combination comprising, two oflices one adjacent each end of said stretch connected by two line wires and each comprising code transmitting apparatus and code responsive apparatus, 'firstand asecon'cl manually controllable "contact device for eacho'f said offices'each having a normal and "a reverse position, means controlle'd'by each of said'first contact devices when operated to its reverse position if the associated second contact device is'ln the normal'position for effecting operation-of the playing the indicationfis line clearfmeans con-- trolled by the code responsive apparatus at said other oifice in response to said first code and controlled by the associated second contact device upon being operated to its reverse position for effecting operation of the associated code transmitting apparatus to transmit a second code over said line wires, and means controlled by the code responsive apparatus at the first ofiice in response to. said second code for displaying the indication line clear received.

, 3. In a signal control system for a stretch of railway track in which signals are located at opposite ends of the stretch for governing trafiic movements over the stretch, the combination comprising, two ofiices one adjacent each end of said stretch connected by two line wires and each including apparatus for transmitting codes oversaid line wires to the other ofiice and for responding to codes transmitted over said line wires from the other office, a first and a second manually controllable contact device for each of said ofiices each having a normal and a reverse position, means controlled by each of said first contact devices if operated to its reverse position while the associated second contact device is in the normal position for effecting operation of the apparatus at its ofiice to transmit a first code over said line wires, means controlled by the apparatus at the other office in response to said first code for displaying the indication is line clear and for transmitting a second code over said line wires if the associated second contact device is operated to its reverse position, means controlled by the second contact device at said other office upon being operated to its reverse position for displaying the indication line clear sent, and means controlled by the apparatus at the first ofiice in response to said second code for displaying the indication line clear received.

4. In a signal control system for a stretch of railway track in which signals are located at opposite ends of the stretch for governing traflic movements over the stretch, the combination comprising, two ofiices one adjacent each end of said stretch connected by two line wires, a first and a second manually controllable contact device at each office each having a normal and a reverse position, means controlled by each of said first contact devices if operated to its reverse position and if the associated second contact device is in the normal position for transmitting a first code over said line wires, means at the other office responsive to said first code for displaying the indication is line clear and for transmitting a second code over said line wires if its associated second contact device is operated to its reverse position, and means at the first office responsive to said second code for displaying the indication line clear received.

5. In a signal control system for a stretch of railway track in which signals are located at opposite ends of the stretch for governing traffic movements over the stretch, the combination comprising, two offices one adjacent each end o{ said stretch connected by two line wires, a first and a second manually controllable contact device at each office each having a normal and a reverse position and said second contact device having a normal lock for locking said second contact device in its normal position when the corresponding lock is deenergized, means controlled by each of said first contact devices if operated to its reverse position and if the associated second contact device is in the normal position for transmitting a first code over said line wires, means at the other ofiice responsive to said first code second contact device, means at said other office controlled by the associated second contact device upon'being operated to its reverse position for transmitting a second code over said line wires, and means at the first ofiice responsive to said second code for displaying the indication line clear received. 6. In a signal control system for a stretch o railway track in which signals are located .at

opposite ends of the stretch for governing traffic movements over the stretch, the combination comprising, two OfiiCGS one adjacent each end of said stretch connected by two line wires, a first and a second manually controllable contact de-.

vice at each ofiice each having a normal and a reverse position and said second contact device, having normal and reverse locks for locking said second contact device in its normal and-reverse positions respectively when the corresponding lock is deenergized, means controlled by each of said first contact devices if operated to its reverse position and if the associated second contact de vice is in the normal position for transmitting a,

means controlled manually and by said second code for clearing a signal adjacent the first ofiice, means responsive to a train upon passing said signal for transmitting a third code over said line wires, and means controlled in part by said third code for energizing the reverse lock for the second contact device at said other office.

7. In a signal control system for a stretch of railway track in which signals are located at opposite end-s of the stretch for governing trafiic movements over the stretch, the combination comprising, two offices one adjacent each end of said stretch connected by two line wires, a first and a second manually controllable contact device Jat each ofiice each having a normal and a reverse position and said second contact device having normal and reverse locks for locking said second contact device in its normal and reverse positions respectively when the corresponding lock is deenergized, means controlled by each of said first contact devices if operated to its reverse position and if the associated second contact device is in the normal position for transmitting a first code over said line wires, means at the other ofiice responsive to said first code for energizing the normal lock for the second contact device at said other ofiice, means at said other ofiice controlled by the associated second contact device upon being operated to its reverse position for transmitting a second code over said line wires, means controlled manually and by said second code for clearing a signal adjacent the first office, and means controlled by a train upon having passed through a short track section adjacent each end of said stretch for energizing the reverse lock for the second contact device at said other ofilce.

8. In a signal control system for a stretch of railway track in which signals are located at opposite ends of the stretch for governing traffic movements over the stretch, the combination comprising, two ofices one adjacent each end of said stretch connected by two line wires, a first for displaying the indication is line clear and for energizing the normal lock for the associatedand a second manually controllable contact device at each oflice each having a normal and a reverse position, means controlled by each of said first contact devices if operated to its reverse position and if the associated second contact device is in the normal position for transmitting a first code over said line wires, means at the other oflice controlled by said first code and by operation of the second contact device at said other office to its reverse position for transmitting a second code over said line wires, a manually operable signal control device at the first ofiice having a normal lock which if deenergized locks said signal control device in a normal position, means controlled by said second code for energizing the normal lock for said signal control device, and means controlled by operation of said signal control device to a reverse position for clearing a signal at the first office and for cancelling the control by said second code so that if the signal is then returned to stop it cannot again be cleared until said second code is again transmitted from said other ofiice.

9. In a signal control system for a stretch of railway track in which signals are located at opposite ends of the stretch for governing trafflc movements over the stretch, the combination comprising, two oflices one adjacent each end of said stretch connected by two line wires, a first and a second manually controllable contact device at each ofiice each having a .normal and .a-

reverse position, means controlled by each of said first contact devices if operated to its reverse position and if the associated second contact device is in the normal position for transmitting a first code over said line wires, means "at the other office controlled by said first code for transmitting a second code over said line wires if the second contact device at said other office is operated to its reverse position, means controlled manually and by said second code for clearing a signal adjacent said first oflice, means responsive to a train upon passing said signal for displaying an indication train on line going" at the first office and for transmitting a third code over said line wires, and means controlled by said third code for displaying an indication train on line coming at said other ofiice.

LESLIE HURST PETER. JAMES PERRIN COLEY. 

